angelscript: Add a test script to surface for Entity as argument.
angelscript: Add time measuring codes to AngelScript invocation.
angelscript: Add EntityRef class to AngelScript.

It may make the script a bit complicated, but execution time is expected
to be reduced.
angelscript: Implement almost identical AngelScript codes to Squirrel.

Measuring result shows that AngelScript is slightly faster than Squirrel,
but not much.  Current codes lacking some functionality, which may make
it look faster, too.